Back light module for use in a dual-sided display

ABSTRACT

A back light module adopted for use in a dual panel display includes a plurality of external electrode fluorescent lamps (EEFLs) positioned between two liquid crystal display panels. Each EEFL has a first electrode and a second electrode, and the first electrodes and the second electrodes are respectively electrically connected in parallel.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a back light module adopted for use ina dual-sided display, and more particularly, to a back light modulehaving a simplified structure.

2. Description of the Prior Art

With the development of liquid crystal display (LCD) technologies, LCDdisplay panels have been widely applied to various consumer electronicproducts such as digital cameras, personal digital assistants, mobilephones, and flat TVs. A back light module, a key component in an LCDdisplay, is installed in the back side of an LCD display panel forproviding the LCD display panel with light.

The back light module substantially includes a plurality of cold cathodefluorescent lamps (CCFL) arranged in parallel, and a combination ofvarious optical components such as diffusion plates and prisms forproviding the LCD display panel with a brilliant and even light source.Cold cathode fluorescent lamps have to be driven by a high AC voltage,and moreover, they have to be respectively driven by differentinverters. If an inverter is used to drive a plurality of cold cathodefluorescent lamps, the ballast of the inverter cannot be maintainedstable, which results in an uneven brightness of the cold cathodefluorescent lamps. As a result, each cold cathode fluorescent lamprequires independent conducting wires to connect to an inverter, andthis limitation increases the difficulty in allocating internalcomponents and in housing design of the LCD. For a single panel LCD, theinverters and the conducting wires can be hidden under the reflectingplate or the rear frame of the back light module without influencing theillumination of the back light module.

However, for a dual-sided display, the allocation of the inverters andthe conducting wires becomes a problem to be solved. The dual-sideddisplay is composed of two parallel LCD display panels, and a back lightmodule installed in between the LCD display panels. Therefore the backlight module has to be open on both sides and a reflecting plate is notallowed. In such a case, the inverters and the conducting wires cannotbe arranged under the reflecting plate, and have to be installedsomewhere inside the back light module without influencing theillumination of the back light module. Generally, the conducting wiresare positioned in the peripheral region of the display, nevertheless,this region is originally designed for other components, such as drivingcircuits of the display. In addition, since each cold cathodefluorescent lamp requires an inverter, the allocation of the internalcomponents for the dual-sided display becomes more difficult.

Please refer to FIG. 1 and FIG. 2. FIG. 1 is a top view of aconventional back light module 10 for use in a dual-sided display, andFIG. 2 is a cross-sectional view of the back light module 10 shown inFIG. 1. As shown in FIG. 1 and FIG. 2, the back light module 10 ispositioned between parallel LCD display panels 20 for providing a lightsource for both of the LCD display panels 20. The back light module 10includes a frame 12, and a plurality of cold cathode fluorescent lamps14 (CCFL) fixed in the frame 12. Each cold cathode fluorescent lamp 14includes two electrodes 14A and 14B exposed outside the frame 12. Inaddition, the back light module 10 further includes a plurality ofinverters 16 corresponding to the cold cathode fluorescent lamps 14 forconverting DC voltage into AC voltage. Each inverter 16 has twoconducting wires 16A and 16B respectively connected to the electrodes14A and 14B so as to provide the cold cathode fluorescent lamps 14 withproper driving voltages. Furthermore, the back light module 10 usuallyincludes two diffusion plates 18, each positioned between the coldcathode fluorescent lamps 14 and the respective LCD display panel 20 forscattering the light beams irradiated by the cold cathode fluorescentlamps 14.

As described, for the conventional back light module 10, the same amountof inverters 16 as cold cathode fluorescent lamps 14 has to be installedto provide corresponding driving voltages. This increase in invertersmeans an increase in cost. Besides, redesigns for extra space forallocating the inverters 16 and the conducting wires 16A and 16Bconflict with dimensional requirements of a small size display. Inaddition, the inverters 16 are high frequency components, and thereforean increase in the amount of inverters 16 generates increasedelectromagnetic interference.

Therefore, any reduction in quantity of inverters for a dual-sideddisplay would result in a more flexible design and effectively economizecost.

SUMMARY OF INVENTION

It is therefore a primary objective of the present invention to providea back light module having a simplified structure for solving theaforementioned problems.

According to a preferred embodiment of the present invention, a backlight module adopted for use in a dualsided display having two parallelLCD display panels is provided. The back light module includes aplurality of external electrode fluorescent lamps (EEFLs) positionedbetween the two LCD display panels. Each external electrode fluorescentlamp includes a first electrode and a second electrode. The firstelectrodes and the second electrodes are electrically connected inparallel separately.

According to a preferred embodiment of the present invention, a backlight module adopted for use in a dualsided display having two parallelLCD display panels is provided. The back light module includes a flatfluorescent lamp positioned between the two LCD display panels, wherethe flat fluorescent lamp is double-faced light source.

Since the back light module of the present invention utilizes externalelectrode fluorescent lamps or a flat fluorescent lamp, which can bedriven by a single inverter, to replace cold cathode fluorescent lampsas the light source of the dual display, the amounts of the invertersand conducting wires are reduced. This reduces the cost and avoidsdifficulty in designing dual-sided displays.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after having read thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of a conventional back light module for use in adual-sided display.

FIG. 2 is a cross-sectional view of the back light module shown in FIG.1.

FIG. 3 is a top view of a back light module according to a firstpreferred embodiment of the present invention

FIG. 4 is a cross-sectional view of the back light module shown in FIG.3.

FIG. 5 is a schematic diagram illustrating another connection method ofthe electrodes.

FIG. 6 is a top view of a back light module according to a secondpreferred embodiment of the present invention.

FIG. 7 is a cross-sectional view of the back light module shown in FIG.6.

FIG. 8 is a top view of a flat fluorescent lamp.

DETAILED DESCRIPTION

Please refer to FIG. 3 and FIG. 4. FIG. 3 is a top view of a back lightmodule 50 according to a first preferred embodiment of the presentinvention, and FIG. 4 is a cross-sectional view of the back light module50 shown in FIG. 3. As shown in FIG. 3 and FIG. 4, the back light module50 is installed in between two parallel LCD display panels 60 forproviding a light source for both of the LCD display panels 60. The backlight module 50 includes a frame 52, and a plurality of externalelectrode fluorescent lamps (EEFLs) 54 fixed to the frame 52. Eachexternal electrode fluorescent lamp 54 includes two electrodes 54A and54B exposed outside the frame 52. In addition, the back light module 50further includes an inverter 56 electrically connected to the electrodes54A and 54B of the external electrode fluorescent lamps 54 through twoconducting wires 56A and 56B so as to provide the external electrodefluorescent lamps 54 with proper driving voltages. It is noted that eachexternal electrode fluorescent lamp 54 has an independent ballast (notshown), and thus all the external electrode fluorescent lamps 54 can bedriven via the inverter 56. The back light module 50 further includestwo diffusion plates 58 respectively positioned between the externalelectrode fluorescent lamps 54 and the two LCD display panels 60 forscattering light generated by the external electrode fluorescent lamps54. In addition, other optical components, such as prisms and brightnessenhancing films, can be installed in the back light module 50 wherenecessary.

As shown in FIG. 3 and FIG. 4, since the back light module 50 utilizesthe external electrode fluorescent lamps 54 as a light source, and has asingle inverter 56 to drive the external electrode fluorescent lamps 54,the electrodes 54A and 54B can be respectively connected to theconducting wires 56A and 56B of the inverter 56 in a parallel manner.Accordingly, the amounts of conductive wires are reduced. In thisembodiment, the electrode 54A of each external electrode fluorescentlamp 54 is connected in parallel to the conducting wire 56A through aconducting wire, and the electrode 54B (not shown) of each externalelectrode fluorescent lamp 54 is connected in parallel to the conductingwire 56B (not shown) through a conducting wire, so that the externalelectrode fluorescent lamps 54 can obtain an AC voltage from theinverter 56. It is noted that the external electrode fluorescent lamps54 are driven by the inverter 56 in a floating manner, which means thetwo electrodes 54A and 54B are driven by voltages out of phase. Forexample, if the driving voltage of the external electrode fluorescentlamps 54 is 1 KV, the floating driving method means the electrodes 54Aand 54B are respectively provided with a +0.5 KV and a −0.5 KV ACvoltage.

The external electrode fluorescent lamps 54 can also be connected inanother parallel manner. Please refer to FIG. 5, which is a schematicdiagram illustrating another connection method of the electrodes 54A. Asshown in FIG. 5, the electrodes 54A are connected in parallel with ametal electrode 59. In practice, the electrodes 54A (or 54B) can beconnected in either way illustrated in FIG. 4 or FIG. 5.

As described, since the back light module 50 utilizes the externalelectrode fluorescent lamps 54 as a light source, only an inverter 56 isrequired. Accordingly, the electrodes 54A and 54B respectively require aconducting wire or a metal electrode 59 to connect to the conductingwires 56A and 56B. Consequently, the amounts of inverters 56 andconducting wires are reduced.

Please refer to FIG. 6 and FIG. 7. FIG. 6 is a top view of a back lightmodule 70 according to a second preferred embodiment of the presentinvention, and FIG. 7 is a cross-sectional view of the back light module70 shown in FIG. 6. As shown in FIG. 6 and FIG. 7, the back light module70 is installed between two parallel LCD display panels 80 for providinga light source for both of the LCD display panels 80. The back lightmodule 70 includes a frame 72, and a double-faced luminous flatfluorescent lamp 74 fixed to the frame 72. The flat fluorescent lamp 74includes two electrodes 74A and 74B. The back light module 70 furtherincludes an inverter 76 connected to the electrodes 74A and 74B of theflat fluorescent lamp 74 through two conducting wires 76A and 76B so asto drive the flat fluorescent lamp 74. The back light module 70 furtherincludes two diffusion plates 78 respectively installed between the flatfluorescent lamp 74 and the two LCD display panels 80 for providing evenillumination. In addition, other optical components, such as prisms andbrightness enhancing films, can be installed in the back light module50.

The flat fluorescent lamp 74 is implemented by various fluorescent lampshaving a curved or a zigzag structure. Please refer to FIG. 8, which isa perspective view of the flat fluorescent lamp 74. As shown in FIG. 8,the flat fluorescent lamp 74 is composed of a fluorescent lamp having azigzag structure, and connected to the inverter (not shown) through theelectrodes 74A and 74B. In addition, the flat fluorescent lamp 74 can beincorporated with a scattering plate (not shown) to improve lightuniformity.

It can be seen that the back light module 70 with a flat fluorescentlamp 74 installed is as efficient as several cold cathode fluorescentlamps. Consequently, the back light module 70 only requires a singleinverter 76 to drive the flat fluorescent lamp 74, and therefore reducethe quantities of the inverter 76 and the conducting wires.

In comparison with the prior art, the back light module according to thepresent invention effectively reduces the amounts of inverters andconducting wires. As a result, the problems of allocating the invertersand conducting wires are solved, and the cost is accordingly reduced.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device may be made while retainingthe teachings of the invention. Accordingly, the above disclosure shouldbe construed as limited only by the metes and bounds of the appendedclaims.

1. A back light module for use in a dual-sided display having twoparallel liquid crystal display (LCD) panels, the back light modulecomprising: a plurality of external electrode fluorescent lamps (EEFLs)positioned between the two LCD display panels, each external electrodefluorescent lamp comprising a first electrode and a second electrode,the first electrodes being electrically connected in parallel, and thesecond electrodes being electrically connected in parallel.
 2. The backlight module of claim 1, wherein the first electrodes and the secondelectrodes are electrically connected to an inverter that supplies an ACvoltage.
 3. The back light module of claim 2, wherein the inverterdrives the external electrode fluorescent lamps in a floating manner. 4.The back light module of claim 1, wherein the first electrodes and thesecond electrodes are respectively connected to a metal electrode. 5.The back light module of claim 4, wherein the metal electrode is aconducting wire.
 6. The back light module of claim 1, further comprisingtwo diffusion plates respectively positioned between the two LCD displaypanels and the external electrode fluorescent lamps.
 7. The back lightmodule of claim 1, further comprising a diffusion plate positionedbetween one of the LCD display panels and the external electrodefluorescent lamps.
 8. The back light module of claim 7, furthercomprising a frame wherein the diffusion plate and the flat fluorescentlamp are fixed to the frame.
 9. A back light module for use in a dualface display having two parallel LCD display panels, the back lightmodule comprising: a flat fluorescent lamp positioned between the twoLCD display panels, the flat fluorescent lamp being a double-faced lightsource.
 10. The back light module of claim 9, wherein the flatfluorescent lamp comprises a first electrode and a second electrodeelectrically connected to an inverter.
 11. The back light module ofclaim 9, further comprising two diffusion plates respectively positionedbetween the two LCD display panels and the flat fluorescent lamp. 12.The back light module of claim 9, further comprising a diffusion platepositioned between one of the LCD display panels and the flatfluorescent lamp.
 13. The back light module of claim 12, furthercomprising a frame wherein the diffusion plate and the flat fluorescentlamp are fixed to the frame.
 14. A back light module for use in a dualface display having two parallel LCD display panels, the back lightmodule comprising: a means for illuminating; and a diffusion platepositioned between the means for illuminating and one of the LCD displaypanels.
 15. The back light module of claim 14, wherein the means forilluminating comprises a plurality of external electrode fluorescentlamps (EEFLs), each external electrode fluorescent lamp comprising afirst electrode and a second electrode, the first electrodes beingelectrically connected in parallel, and the second electrodes beingelectrically connected in parallel.
 16. The back light module of claim15, wherein the first electrodes and the second electrodes areelectrically connected to an inverter that supplies an AC voltage to theexternal electrode fluorescent lamps.
 17. The back light module of claim16, wherein the inverter drives the external electrode fluorescent lampsin a floating manner.
 18. The back light module of claim 15, wherein thefirst electrodes and the second electrodes are respectively connected toa metal electrode.
 19. The back light module of claim 18, wherein eachmetal electrode is a conducting wire.
 20. The back light module of claim15, further comprising a frame wherein the diffusion plate and the flatfluorescent lamp are fixed to the frame.
 21. The back light module ofclaim 14, wherein the means for illuminating is a flat fluorescent lamp,and the flat fluorescent lamp is a double-faced light source.
 22. Theback light module of claim 21, wherein the flat fluorescent lampcomprises a first electrode and a second electrode electricallyconnected to an inverter.
 23. The back light module of claim 21, furthercomprising a frame wherein the diffusion plate and the flat fluorescentlamp are fixed to the frame.